A112924 Number of nonisomorphic connected Y-graphs Y(n:i,j,k) with girth 6 on 4n vertices (or nodes) for 1<=i,j,k<=n.

0, 0, 0, 1, 3, 2, 3, 2, 5, 3, 6, 6, 4, 4, 8, 12, 9, 4, 12, 10, 11, 19, 10, 12, 15, 12, 14, 22, 15, 12, 20, 16, 18, 31, 18, 18, 24, 16, 20, 50, 21, 20, 28, 22, 23, 50, 27, 24, 32, 24, 26

Offset

3,5

Comments

A Y-graph Y(n:i,j,k) has 4n vertices arranged in four segments of n vertices. Let the vertices be v_{x,y} for x=0,1,2,3 and y in the integers modulo n. The edges are v_{1,y}v_{1,y+i}, v_{2,y}v_{2,y+j}, v_{2,y}v_{2,y+k} and v_{0,y}v_{x,y}, where y=0,1,...,n-1 and x=1,2,3 and the subscript addition is performed modulo n.

References

I. Z. Bouwer, W. W. Chernoff, B. Monson and Z. Starr (Editors), "Foster's Census", Charles Babbage Research Centre, Winnipeg, 1988.

J. D. Horton and I. Z. Bouwer, Symmetric Y-graphs and H-graphs, J. Comb. Theory B 53 (1991) 114-129

Links

Table of n, a(n) for n=3..53.

Example

Y(6:1,1,1) is the smallest Y-graph with girth 6.

Crossrefs

Cf. A112921, A112922, A112923.

Sequence in context: A238393 A092962 A258778 * A267148 A367682 A230406

Adjacent sequences: A112921 A112922 A112923 * A112925 A112926 A112927

Keyword

nonn

Author

Marko Boben (Marko.Boben(AT)fmf.uni-lj.si), Tomaz Pisanski and Arjana Zitnik (Arjana.Zitnik(AT)fmf.uni-lj.si), Oct 06 2005

Status

approved